Exposure to very large heat fluxes as well as large radiation loads inducing strong wear threatens to limit the lifetime of solid plasma facing component materials in fusion energy devices. Liquid metal devices, however, do not suffer the same ill effects. Liquid lithium, in particular, has shown promise as a potential candidate for a plasma facing component material. Several methods exist to introduce lithium into fusion devices, however, one of the most unique methods of doing so is the Liquid-Metal Infused Trenches concept of CPMI. LiMIT relies on thermoelectric magnetohydrodynamics (TEMHD) to propel a liquid metal down a series of trenches. TEMHD flow is based on the interaction of a thermoelectric current with a magnetic field.
The source of the thermoelectric current in the LiMIT device arises from the junction between the flowing liquid metal and the trench wall material. A thermal gradient across this interface gives rise to the thermoelectric current. An analogy may be constructed by considering the interface to be composed of two junctions, the top portion of the trench would constitute the hot junction of a thermocouple, while the bottom portion of the trench would constitute the cold junction. Since the interfacial voltage between the two materials is a function of temperature, the temperature difference gives rise to a voltage difference, which drives a current.
The magnitude of the current driven is proportional to the relative thermopower, or the difference in Seebeck coefficient, between the two materials. To generate data on the Seebeck coefficient of a wide variety of materials, an apparatus was constructed at CPMI. Shown in the photo above, measurement of the Seebeck coefficient of many fusion relevant materials is possible. A library of Seebeck coefficients is being compiled, and measurements are ongoing.